Cure-accelerator for epoxy resin

ABSTRACT

A cure-accelerator for an epoxy resin, which comprises a compound of the formula (I),R1R2NCONH-Ar-NECONR3R4(I)wherein R1, R2, R3 and R4 are C1-C3 lower alkyl groups which may be the same or different, and Ar is a substituted tolylene group of the formula (II)   &lt;IMAGE&gt;   (wherein R5 and R6 are C1-C4 lower alkyl groups which may be the same or different) or a 1,5-naphthylene group.

This is a Division, of application Ser. No. 08/629,223 filed on Apr. 8,1996 now U.S. Pat. No. 5,719,320.

The present invention relates to a cure-accelerator for an epoxy resin,which does not contain a halogen atom in a molecule and which is capableof curing an epoxy resin at a low temperature when it is added to asystem comprising an epoxy resin and dicyandiamide. Also, the presentinvention relates to a novel urea derivative useful as acure-accelerator for an epoxy resin.

An epoxy resin is excellent in various properties such as adhesiveproperties, mechanical strength and electric insulating properties, andis applicable to various uses having various functions when it is usedin combination with a substrate resin, a curing agent, a modifier, anaccelerator or the like. Thus, an epoxy resin is used in various manyfields such as a paint, an adhesive, a sealing compound for electronicmaterials and a carbon fiber-composite material (hereinafter referred toas "CFRP"). Recently, a demand for an epoxy resin was diversified invarious fields, and researches and developments have been conducted soas to satisfy the demand for various high performances.

An epoxy resin composition generally used, employs a two-pack systemcomprising a main pack and a curing agent pack. The main pack and thecuring agent pack are stored separately, and are mixed each other at thetime of using. The two-pack system composition is cured at roomtemperature, but has various disadvantages that a blending mistake issometimes caused by an operator and that a pot life is limited. In orderto overcome these disadvantages, a latent curing agent for one-pack typeepoxy resin (a curing agent which does not react with an epoxy resin inthe vicinity of room temperature but rapidly reacts with the epoxy resinwhen heated to a predetermined temperature) is developed. This type of alatent curing agent is dispersed in an epoxy resin, and is known to bedissolved in the presence of heat. A typical example is dicyandiamide.However, curing of this system employing this compound is slow, and itis necessary to cure this system at a high temperature. On the otherhand, in order to make it applicable to various uses, the curingtemperature must be made low. Also, the lowering of the curingtemperature provides an advantage of saving energy. Under thesecircumstances, a cure-accelerator to remove the above-mentioneddisadvantage of the dicyandiamide is demanded.

Examples of a cure-accelerator known at present, include a ureacompound, an imidazole compound and the like, and more particulartypical examples include 3-(3,4-dichlorophenyl)-1,1-dimethylurea(hereinafter referred to as "DCMU"), 2-methylimidazole, and the like.However, the reactivity of an epoxy resin composition is increased inthe presence of a curing agent, whereas a preservation stability(can-stability) of an epoxy resin composition is lowered, and asatisfactory composition of satisfying both the curing property and thepreservation stability at the same time has not been developed up tonow. Also, a compound containing a halogen atom provides a problem ofcorroding a metal when it is used as a sealing compound for electronicmaterials. Thus, there are problems to be solved in this field.

Some inventions have been made to meet the above-mentioned variousdemands. For example, Japanese Examined Patent Publication No.44768/1987 discloses to improve a low temperature curability and apreservation stability by using DCMU as a cure-accelerator for a carbonfiber-reinforced epoxy resin composition without reducingheat-resistance of a cured resin. However, since DCMU contains a halogenatom in a molecule, it is hardly usable for an electronic material fieldand provides an environmental problem. Also, Japanese Unexamined PatentPublication No. 310890/1993 employs the above-mentioned urea compoundfor a composite material prepreg, but this is hardly usable for anelectronic material field and provides an environmental problem on thesame grounds as mentioned above.

Under these circumstances, an object of the present invention is toprovide a cure-accelerator to be added to a thermoset resin compositionbased on an epoxy resin and dicyandiamide, which does not contain ahalogen atom in a molecule and provides a satisfactory preservationstability and an excellent low temperature curability.

In order to achieve the above-mentioned object, we have studied variousurea derivatives, and as the result of this study, we have discovered anovel urea derivative containing no halogen atom usable as acure-accelerator for an epoxy resin, and also discovered that a group ofurea derivatives containing no halogen atom are suitable as acure-accelerator for an epoxy resin, which has a satisfactorypreservation stability and an excellent low temperature curability.

Thus, the present invention provides a cure-accelerator for an epoxyresin, which comprises a compound of the formula (I),

    R.sub.1 R.sub.2 NCONH--Ar--NHCONR.sub.3 R.sub.4            (I)

wherein R₁, R₂, R₃ and R₄ are C₁ -C₃ lower alkyl groups which may be thesame or different, and Ar is a substituted tolylene group of the formula(II) ##STR2## (wherein R₅ and R₆ are C₁ -C₄ lower alkyl groups which maybe the same or different) or a 1,5-naphthylene group.

Further, the present invention provides a method for curing an epoxyresin, characterized by using the above-mentioned urea derivativecompound.

Still further, the present invention provides a novel urea derivativeuseful as a cure-accelerator for an epoxy resin, which has the formula(I),

    R.sub.1 R.sub.2 NCONH--Ar--NHCONR.sub.3 R.sub.4            (I)

wherein R₁, R₂, R₃ and R₄ methyl groups and Ar is a substituted tolylenegroup of the formula (II) ##STR3## (wherein R₅ and R₆ are lower alkylgroups having a carbon number of from 1 to 4 which may be the same ordifferent).

Particularly, a preferable cure-accelerator for an epoxy resin is a ureaderivative compound of the formula (I) wherein R₁, R₂, R₃ and R₄ aremethyl groups and Ar is ##STR4##

The urea derivative compound of the formula (I) wherein R₁, R₂, R₃ andR₄ are methyl groups and Ar is a substituted tolylene group of theformula (II) ##STR5## (wherein R₅ and R₆ are C₁ -C₄ lower alkyl groupswhich may be the same or different) is a novel compound, and isexpressed by the formula (I-A), ##STR6## (wherein R₅ and R₆ are asdefined above).

The novel urea derivative compound of the formula (I-A) of the presentinvention can be produced in accordance with the following methods, i.e.(i) a method which comprises reacting at least stoichiometric amount ofN,N-dimethylcarbamoyl chloride with a dialkyltoluenediamine in thepresence of an organic base or inorganic base and/or a phase transfercatalyst in an inert organic solvent or (ii) a method which comprisestreating a dialkyltoluenediamine with phosgene to form adialkyltoluenediisocyanate and reacting at least stoichiometric amountof dimethylamine with the dialkyltoluenediisocyanate.

In the novel urea derivatives of the formula (I-A) of the presentinvention, R₅ and R₆ are C₁ -C₄ lower alkyl groups, examples of whichinclude a methyl group, an ethyl group, a propyl group, an isopropylgroup, a n-butyl group, an isobutyl group, a tertiary butyl group andthe like, and among them, an ethyl group is most preferable.

Examples of the novel urea derivatives of the formula (I-A) of thepresent invention are illustrated as follows:

(a) 2,4,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene,

(b) 2,5,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene,

(c) 2,4,5-trimethyl-1,3-bis(3,3-dimethylureido)benzene,

(d) 2,4-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(e) 2,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(f) 4,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(g) 4,5-diethyl-2-methyl-1,3-bis(3,3-dimethylureido)benzene,

(h) 2,4-dipropyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(i) 2,5-dipropyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(j) 4,5-dipropyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(k) 4,5-dipropyl-2-methyl-1,3-bis(3,3-dimethylureido)benzene,

(l) 2,4-diisopropyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(m) 4,5-diisopropyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(n) 2,4-dibutyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(o) 2,5-dibutyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(p) 4,5-dibutyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene,

(q) 4,5-dibutyl-2-methyl-1,3-bis(3,3-dimethylureido)benzene,

(r) 2,5-di-tert-butyl-6-methyl-1,3-bis(3,3-dimethylureido) benzene,

(s) 4,5-di-tert-butyl-6-methyl-1,3-bis(3,3-dimethylureido )benzene,

(t) 4-ethyl-2,5-dimethyl-1,3-bis(3,3-dimethylureido)benzene,

(u) 5-ethyl-2,4-dimethyl-1,3-bis(3,3-dimethylureido)benzene,

(v) 2-ethyl-6-methyl-4-propyl-1, 3-bis (3,3-dimethylureido)benzene, and

(w) 2-ethyl-6-methyl-5-butyl-1,3-bis(3,3-dimethylureido)benzene.

Also, in the present invention, a urea derivative compound of theformula (I) wherein Ar is a 1,5-naphthylene group, is expressed by theformula (I-B), ##STR7## (wherein R₁, R₂, R₃ and R₄ are C₁ -C₃ loweralkyl groups), and this compound can be produced in accordance with thefollowing methods, i.e. (i) a method which comprises reacting at leaststoichiometric amount of a di-lower alkylamine having a desired alkylgroup with naphthylene-1,5-diisocyanate, or (ii) a method whichcomprises reacting at least stoichiometric amount of a N,N-di-loweralkylcarbamoyl chloride having a desired alkyl group withnaphthylene-1,5-diamine in the presence of an organic base or inorganicbase and/or a phase transfer catalyst in an inert organic solvent.

In the urea derivatives of the formula (I-B) of the present invention,R₁, R₂, R₃ and R₄ are lower alkyl groups, examples of which include amethyl group, an ethyl group, a propyl group, an isopropyl group and thelike.

Examples of the urea derivatives of the formula (I-B) of the presentinvention are illustrated as follows:

(1) 1,5-bis(3,3-dimethylureido)naphthalene,

(2) 1,5-bis(3,3-diethylureido)naphthalene,

(3) 1,5-bis(3,3-dipropylureido)naphthalene,

(4) 1,5-bis(3,3-diisopropylureido)naphthalene,

(5) 1,5-bis(3-ethyl-3-methylureido)naphthalene,

(6) 1,5-bis(3-methyl-3-propylureido)naphthalene,

(7) 1,5-bis(3-isopropyl-3-methylureido)naphthalene,

(8) 1,5-bis(3-ethyl-3-propylureido)naphthalene,

(9) 1,5-bis(3-ethyl-3-isopropylureido)naphthalene,

(10) 1,5-bis(3-isopropyl-3-propylureido)naphthalene,

(11) 1-(3,3-dimethylureido)-5-(3,3-diethylureido)naphthalene,

(12) 1-(3,3-dimethylureido)-5-(3,3-dipropylureido)naphthalene, and

(13) 1-(3,3-dimethylureido)-5-(3-ethyl-3-methylureido)naphthalene.

The cure-accelerating effect by the urea derivative compound of thepresent invention is achieved with regard to a resin compositioncomprising a commercially available epoxy resin, dicyandiamide and thecure-accelerator of the present invention. In this case, othercure-accelerators may be additionally incorporated in the resincomposition.

All of various known epoxy resins are usable as an epoxy resin used inthe present invention, and the epoxy resin used in the present inventionis not specially limited, but a preferable example is an epoxy resinhaving at least 2 epoxy groups, such as bisphenol A diglycidyl ether(Ep-808, Ep-827 and Ep-828 manufactured by Shell Chemical Co., Ltd.).

An epoxy resin composition is prepared by blending (A) an epoxy resin,(B) dicyandiamide and (C) a cure-accelerator, and the effect of thecure-accelerator of the present invention can be easily evaluated bymeasuring reaction heat by means of a differential scanning calorimeter(hereinafter referred to as "DSC") (Adv. Polym. Soc. 72, 112-154).

The blending amount of (B) dicyandiamide is from 2 to 15 parts byweight, preferably from 3 to 12 parts by weight, to 100 parts by weightof (A) an epoxy resin. If the blending amount of the component (B) issmaller than 2 parts by weight, curability becomes poor, and if theblending amount of the component (B) exceeds 15 parts by weight, heatresistance is lowered.

The blending amount of (C) a cure-accelerator is from 1 to 20 parts byweight, preferably from 3 to 12 parts by weight, to 100 parts by weightof (A) an epoxy resin. If the blending amount of the component (C) isless than 1 part by weight, low temperature curability becomes poor, andif the blending amount of the component (C) exceeds 20 parts by weight,heat resistance is lowered.

The epoxy resin composition of the present invention may be used incombination with the following additives depending on its use, such as aplasticizer, an organic solvent, a viscosity modifier, a fluiditymodifier, a filler, a bulking agent, a pigment, a dye, a microbicide, ananti-oxidant and the like.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

Example 1

Preparation of diethyl-methyl-1,3-bis(3,3-dimethylureido)benzene

400 ml of toluene, 50 g (0.281 mol) of diethyltoluenediamine (product ofAldemal Asano) and 68.2 g (0.674 mol) of triethylamine were charged in a1l four-forked flask equipped with a condenser, a thermometer and astirrer, and 66.5 g (0.619 mol) of N,N-dimethylcarbamoyl chloride wasdropwise added therein at 10-20° C. for 1 hour. After finishing thedropwise adding, the resultant mixture was slowly heated, and wasreacted at 80° C. for 3 hours. Thereafter, the reaction mixture wascooled to 10° C., and 200 ml of water was added therein under fullystirring. The resultant mixture was then filtrated, and was washed withwater, and was dried to obtain 71.9 g of an aimed product (yield: 80%).

Elemental analysis values of the product were as follows:

    ______________________________________                C         H      N    ______________________________________    Theoretical value                  63.75       8.75   17.50    Experimental value                  63.67       8.80   17.52    ______________________________________

Result of IR(KBr) measurement: ν(C═O) 1638 cm⁻¹.

Example 2

10 g of an epoxy resin (Epikote-828, Yuka-Shell epoxy product), 0.7 g ofdicyandiamide (Dyhard 100S SKW, Trostberg product) and 0.7 g ofdiethyl-methyl-1,3-bis(3,3-dimethylureido)benzene (cure-accelerator)prepared in Example 1 were fully blended and dispersed at roomtemperature. The reaction heat of the epoxy composition thus blended wasmeasured by means of DSC, and it was recognized that the exothermic peakwas 147° C. and that the composition was cured at this temperature. Theresults are shown in the following Table 1.

Example 3

The same procedure as in Example 2 was repeated, except that the amountof the cure-accelerator was changed, and the results are shown in thefollowing Table 1.

Example 4

Preparation of 1,5-bis(3,3-dimethylureido)naphthalene

300 ml of toluene and 102.9 g (1.143 mol) of 50 wt % of dimethylamineaqueous solution were charged in a 1l four-forked flask equipped with acondenser, a thermometer and a stirrer, and a solution having 100 g(0.476 mol) of naphthalene-1,5-diisocyanate completely dissolved in 500ml of toluene was dropwise added therein under stirring at 15°-20° C.for 30 minutes. After finishing the dropwise addition, the resultantmixture was slowly heated, and was reacted at 50° C. for 5 hours toprecipitate a crystal. The crystal thus precipitated was filtrated,washed with water and dried to obtain 139 g of an aimed product (yield:97%).

Elemental analysis values were as follows:

    ______________________________________                C         H      N    ______________________________________    Theoretical value                  64.00       6.67   18.67    Experimental value                  64.03       6.65   18.70    ______________________________________

As the result of IR(KBr) measurement, ν(C═O) was 1642 cm⁻¹, and --NCOabsorption of 2280 cm⁻¹ was not recognized.

Example 5

Preparation of 1,5-bis(3,3-diethylureido)naphthalene

300 ml of toluene and 83.6 g (1.143 mol) of diethylamine were charged inthe same type of flask as used in Example 4, and a solution having 100 g(0.476 mol) of naphthalene-1,5-diisocyanate completely dissolved in 500ml of toluene was dropwise added therein under stirring at 15°-20° C.for 30 minutes. After finishing the dropwise addition, the resultantmixture was slowly heated, and was reacted at 50° C. for 5 hours toprecipitate a crystal. The crystal thus precipitated was filtrated,washed with water and dried to obtain 153.0 g of an aimed product(yield: 98%) having a melting point (DSC) of 223° C.

Elemental analysis values were as follows:

    ______________________________________                C         H      N    ______________________________________    Theoretical value                  65.85       7.32   17.07    Experimental value                  65.80       7.33   17.05    ______________________________________

As the result of IR(KBr) measurement, ν(C═O) was 1622 cm⁻¹, and --NCOabsorption of 2280 cm⁻¹ was not recognized.

Example 6

10 g of an epoxy resin (Epikote-828, Yuka-Shell epoxy product), 0.7 g ofdicyandiamide (Dyhard 100S SKW, Trostberg product) and 0.7 g of1,5-bis(3,3-dimethylureido)naphthalene (cure-accelerator) prepared inExample 4 were fully blended and dispersed at room temperature. Thereaction heat of the epoxy composition thus blended was measured bymeans of DSC, and it was recognized that the exothermic peak was 149° C.and that the epoxy composition was cured at this temperature. Theresults are shown in the following Table 1.

Example 7

The same procedure as in Example 6 was repeated, except that the amountof the cure-accelerator was changed. The results are shown in thefollowing Table 1.

Example 8

The same procedure as in Example 6 was repeated, except that 0.7 g of1,5-bis(3,3-diethylureido)naphthalene prepared in Example 5 was used asa cure-accelerator in place of the cure-accelerator used in Example 6.The results are shown in the following Table 1.

Example 9

The same procedure as in Example 8 was repeated, except that the amountof the cure-accelerator was changed. The results are shown in thefollowing Table 1.

Comparative Example 1

10 g of an epoxy resin (Epikote-828, Yuka-Shell epoxy product) and 0.7 gof dicyandiamide (Dyhard 100S SKW, Trostberg product) were fully blendedand dispersed without adding a cure-accelerator. The reaction heat ofthe epoxy resin composition thus blended was measured by means of DSC,and it was recognized that the exothermic peak was 199° C. and that theepoxy resin composition was cured at this temperature. The results areshown in the following Table 1.

Comparative Example 2

The same procedure as in Example 6 was repeated, except that 0.7 g ofDCMU (Hodogaya Chemical Co. product) was used as a cure-accelerator inplace of the cure-accelerator used in Example 6. The results are shownin the following Table 1.

                                      TABLE 1    __________________________________________________________________________    Epoxy      Dicyan-    Halogen                               Change in epoxy    resin      diamide    atom in                               resin   Curing    (Epikote-  (Dyhard                   Cure-  cure-                               composition as                                       temp.    828)       100S)                   accelerator                          accelerator                               a lapse of time                                       (°C.)    __________________________________________________________________________    Example 2          10 g 0.7 g                   Urea   Nil  No viscosity                                       147                   derivative  increase after                   of Example 1                               a lapse of two                   0.7 g       months at room                               temperature    Example 3          10 g 0.7 g                   Urea   Nil  No viscosity                                       145                   derivative  increase after                   of Example 1                               a lapse of two                   1.0 g       months at room                               temperature    Example 6          10 g 0.7 g                   Urea   Nil  No viscosity                                       149                   derivative  increase after                   of Example 4                               a lapse of two                   0.7 g       months at room                               temperature    Example 7          10 g 0.8 g                   Urea   Nil  No viscosity                                       148                   derivative  increase after                   of Example 4                               a lapse of two                   0.8 g       months at room                               temperature    Example 8          10 g 0.7 g                   Urea   Nil  No viscosity                                       171                   derivative  increase after                   of Example 5                               a lapse of two                   0.7 g       months at room                               temperature    Example 9          10 g 0.8 g                   Urea   Nil  No viscosity                                       169                   derivative  increase after                   of Example 5                               a lapse of two                   1.0 g       months at room                               temperature    Comparative          10 g 0.7 g                   Nil    --   No viscosity                                       199    Example 1                  increase after                               a lapse of two                               months at room                               temperature    Comparative          10 g 0.7 g                   DCMU   Presence                               No viscosity                                       153    Example 2      0.7 g       increase after                               a lapse of two                               months at room                               temperature    __________________________________________________________________________

By using the urea derivatives of the present invention as acure-accelerator for an epoxy resin, the epoxy resin can be cured at alow temperaure and the preservation stability of the epoxy resin can beimproved. Also, since the cure-accelerator of the present invention doesnot contain a halogen atom in a molecule, the epoxy resin containing thecure-accelerator of the present invention provides various excellentproperties when it is used as a paint, an adhesive or a CFRP,particularly as a sealing compound for electronic materials.

I claim:
 1. A cure accelerator for an epoxy resin selected from thegroup consisting of(a)2,4,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene, (b)2,5,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene, (c)2,4,5-trimethyl-1,3-bis(3,3-dimethylureido)benzene, (d)2,4-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, (e)2,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, (f)4,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, and (g)4,5-diethyl-2-methyl-1,3-bis(3,3-dimethylureido)benzene.
 2. A cureaccelerator for an epoxy resin selected from the group consisting of(a)2,4-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, (b)2,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, (c)4,5-diethyl-6-methyl-1,3-bis(3,3-dimethylureido)benzene, and (d)4,5-diethyl-2-methyl-1,3-bis(3,3-dimethylureido)benzene.
 3. A cureaccelerator for an epoxy resin selected from the group consisting of(a)2,4,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene, (b)2,5,6-trimethyl-1,3-bis(3,3-dimethylureido)benzene, and (c)2,4,5-trimethyl-1,3-bis(3,3-dimethylureido)benzene.